1. Field of the Invention
The present invention relates to a device for improving the feed of diesel engines at low temperatures, particularly at temperatures lower than the clouding point of gas oils without modifying the specific chemical characteristics of the gas oil.
2. Discussion of the Background
The use of gas oil in diesel engines at temperatures lower than the cloud point temperature raises a number of operating problems linked to clogging of the filter. The clouding point corresponds to the temperature where crystallization of the paraffins occurs within the gas oil. For temperatures less than this clouding point temperature, if no heating means are provided, these paraffins will be stopped by the fuel filter, during operation of the engine, and will concentrate until the filter is clogged, thus causing a stoppage of the engine through lack of feed.
A solution for overcoming these drawbacks is to modify the specifications of the engine gas oil depending on the seasons, i.e. the clouding point, the flow point and the limit temperature of filterability. For economic reasons, gas oils never have characteristics sufficient for complying with the operating requirements imposed by the lowest temperatures met with. Thus, if it is desired to eliminate all the operating problems of diesel engines at low temperatures, heating devices will have to be associated therewith.
A heating device for recycling the excess gas oil flow from the injection pump, called "scavenging flow", upstream of the fuel filter, by means of a thermostatic valve is disclosed in the French patent application No. 2 456 223, filed in the name of ELF UNION. In this device, after a short operating time of the engine, the gas oil from the scavenging flow has reached a sufficient temperature so that, mixed with the gas oil coming from the reservoir, the mixture is fed to the injection pump at about 25.degree. Celsius. The thermostatic element then regulates the scavenging flow so as to maintain the temperature constant while recycling a more or less large amount of gas oil to the reservoir. For temperatures greater than 25.degree. Celsius, the thermostatic element recycles the entire scavenging flow to the reservoir. Under these circumstances, the gas oil, still at temperatures close to the clouding point in the reservoir, will be fed directly from the reservoir to the thermostatic element, the filter then the high pressure pump, which causes an oscillatory phenomenon which further slows down heating of the gas oil contained in the reservoir.
A device is also known, from French patent application No. 2 256 323, for preheating the gas oil using the exhaust gases of the engine in an exchanger before feeding it into the injection pump. However, this device plays the same role as the preceding device using the scavenging flow and does not solve the problem of heating the gas oil in the reservoir and cooling of the injection pump by the scavenging flow.